With an increase in usage and deployment of optical networks, network reliability, scaling, and costs have become serious problems in providing communication services. Currently, to add capacity to a network, providers must go through a painstaking and time-consuming effort to build out the network offline. That process is further complicated because there is no convenient time for an optical network to be out of service. Original deployment can also be a problem as equipment providers often limit solution offerings to entire networks comprising proprietary components and do not provide for inter-working with other vendors' products. Proprietary components act as a further limiting factor for network growth.
Photonic layers of today's optical networks often are vendor dependent and have proprietary interfaces. Each vendor independently optimizes each individual component and sells full proprietary solutions, often without leveraging standardized platforms. However, advances in technology have reduced transmission limitations, increased the number of wavelengths that can be sent down a fiber, improved amplification techniques, performance, protection and redundancy of the network.
Until recently, transport was provided at the core of the network and provided only point-to-point transport services. A strong shift in revenue opportunities, changing traffic patterns from the enterprise customer, and capabilities to drive optical fiber into metropolitan (metro) areas has opened up additional applications of optical networking.
As is known in the art, a traditional service provider network includes a plurality of processing sites generally referred to as nodes connected by one or more physical and/or logical connections. When the connections establish transmission of a signal between the nodes, the connections are generally referred to as links. Each node typically performs a switching function and one or more additional functions. The nodes may be coupled together in a variety of different network structures.
FIG. 1 shows a state of the art optical network architecture. The architecture includes reconfigurable optical add-drop multiplexers (ROADMs) (104, 110, 122, 124, 112). Operators can send soft commands to the ROADMs to remotely reconfigure them. The ROADMs can drop or add wavelengths without interrupting the ‘pass-through’ channels. The ROADMs are located in major cities for adding and dropping traffic. In between cities, the ROADMs are linked by optical transport networks of optical fibers (128, 120) and amplifiers (106, 126).
The transmission of a signal from a first or source node to a second or destination node may involve the transmission of the signal through a plurality of intermediate links and nodes coupled between the source node and the destination node. FIG. 1 shows such a plurality of links (128, 120) and nodes (100, 108,114, 130, 118). The succession of links and nodes between a source node 100 and a destination node 114 is referred to as a path (128, 120). This example path starts at the transponder 102 (described in detail below) to ROADM 104 and continues through the link 128 and then through the ROADM 110, through the link 120 and to the transponder 116 to the destination switch 114.
FIG. 2 shows more detail on how a client, such as the switches (200, 224), is connected to a state of the art network. Short reach hot pluggable interfaces (202, 206, 218, and 222) are frequently used in connecting clients because they can be inserted or removed from a live network without disturbing other in-service channels. These interfaces facilitate keeping and installing ready-to-use spares, which in turn reduces the amount of redundancy needed for related components. Another advantage of hot pluggable interfaces is lower cost, as they are a standard for multiple vendors and are flexible since they work with a variety of equipment and vendors' products.
Transponders (208, 216) are automatic devices that receive, regenerate, and retransmit a signal on a different wavelength. For example, a transponder can translate a short reach client signal into a long reach line signal. The transponder, while extremely necessary in optical networks, is a high cost component and many of them are needed relative to the quantities of other equipment in the network. Current architecture somewhat reduces the number of transponders needed by allowing optical expressing and selective regeneration to clean up noise at ROADM nodes. Because the transponders are so prevalent in the network and they are so expensive, there is a need to further reduce the number of transponders.
Short reach hot pluggable interfaces (202, 206, 218, 222) are used on the switches (200, 224) and the WDM transponder (208, 216) with “grey” optics (204, 220) in between. The connection 204, 220 between pairs of short reach hot pluggable interfaces is a low grade optical connection. This connection includes grey optics, a low cost laser lacking good wavelength control and stabilization. From the WDM transponder 208, the signal is multiplexed by the optical MULTIPLEXER 210 and transmitted through the optical line 214, including amplifiers and ROADMs (not shown in detail here). The signal is demultiplexed by the optical DEMULTIPLEXER 212 on the other side of the network and then again translated by a WDM transponder 216 and sent through grey optics 220 and the short reach hot pluggable interface 222 to the switch 224.
The optical network shown in FIG. 1 and FIG. 2 may be a Synchronous Optical Network (SONET). SONET is both a standard and a set of specifications for building high speed, digital communications networks that run over fiber-optic cables while interfacing with existing electrical protocols and asynchronous transmission equipment. The use of fiber-optics in such networks provides a dramatic increase in available bandwidth. Bandwidth is currently estimated in the hundreds of gigabits per second. One of the principal benefits of SONET is that it allows for the direct multiplexing of current network services, such as DS1, DS1C, DS2, and DS3, into the synchronous payload of Synchronous Transport Signals (STS). The STS provide an electrical interface that is used as a multiplexing mechanism within SONET Network Elements (NE). In the SONET multiplexing format, the basic signal transmission rate, i.e., STS-1, operates at 51.84 million bits per second. STS-1 can carry 28 DS1 signals or one asynchronous DS3. STS-1 signals are then multiplexed to produce higher bit rates STS-2, STS-3, etc. This is referred to as grooming. SONET signal levels are also defined in terms of an optical carrier (OC). Since the bit rates are the same in each case, the bit rate of STS-1 equals the bit rate of OC-1 with the only difference relating to the type of signal that is being referenced.
In a DWDM network, intermediate optical amplification sites may allow for the dropping and adding of certain wavelength channels. In most recent networks, this is done infrequently, because adding or dropping wavelengths requires manually inserting or replacing wavelength-selective cards. This is costly, and in some networks requires that all active traffic be removed from the DWDM network, because inserting or removing the wavelength-specific cards interrupts the multi-wavelength optical signal.
Flexibility is an important feature in network architecture. Networks today must support a variety of traffic types, including legacy traffic based on regional SONET ring structures that require multiple traffic adds/drops (that is, voice, asynchronous transfer mode [ATM], frame relay). At the same time, those networks must support high-speed Internet backbones which typically act as express lanes requiring little add/drop multiplexing. Networks today combine long haul and short haul traffic for better network flexibility.
A reduction in the cost of bandwidth is an important goal for a successful network. In conventional long-haul technology, the transmission signals must be regenerated every 500 km or so to overcome signal distortion due to dispersion and nonlinear effects and to overcome the build-up of noise generated within the amplifiers. This regeneration is often accomplished through optical-to-electrical-to-optical (O-E-O) conversion, the signal being regenerated during the electrical phase. Regeneration equipment is required on a per-channel basis and is, therefore, very expensive, and it also requires a large equipment footprint and high electrical power consumption and subsequent site climate control. Any reduction in regeneration equipment would result in a significant cost saving.
Control functions and interconnection mechanisms are important attributes of any network. Those attributes permit provisioning, routing, and control across disparate types of underlying transport technologies, such as IP, ATM, SONET/SDH, and DWDM. Control and interconnection are complicated because each transport technology has its own control protocols, and therefore cannot communicate directly. Often provisioning in today's hybrid networks must be done manually by a technician having knowledge of each technology domain.
Reducing complexity by providing a single access method to provision across the entire optical transport network would be highly desirable. Provisioning across multiple-vendor domains within the transport network would save in operations costs and capital costs. The word “thin” is used to denote architectures or architectural components having little complexity and low costs.
One strategy for alleviating the multi-vendor problem is providing a standard or general control plane. Generalized Multiprotocol Label Switching (GMPLS) is an example of that strategy which uses general addressing between legacy and new networks and even heterogeneous networks. GMPLS is an example of a control plane that represents a standard protocol for optical transport network elements. Such a standard protocol could be used to support functions responsible for path setup/teardown, link management and resource accounting. Standards-based protocols allow network providers a substantial cost savings by enabling them to introduce any vendor equipment into any given domain.
As IP-based services expand and traffic increases, there is a need for more cost effective network architectures. The cost associated with building and operating multiple overlay networks has become an impeding factor for traditional service providers to stay competitive. There therefore remains a need for a cost-effective technique to improve operations and provisioning cycles, provide for scalability and limit infrastructure expense, while minimizing the above-described disadvantages.